In industrial monoclonal antibody production affinity chromatography with protein A is usually applied as the first purification step. Protein A chromatography has several advantages, e.g. it is a very robust and efficient unit operation to remove various contaminants like host cell proteins and DNA. However, trace amounts of the immobilized protein A leach and the clearance of the leached ligand must be carefully monitored throughout the process. Even if the new B-domain derived alkaline resistant Protein A resin, MabSelect SuRe™, has shown significantly lower leaching levels than traditional protein A resins the ligand leaching has to be qualified with a validated assay. In this paper we show the properties of commercial ELISAs in quantification of the SuRe-ligand.